Some communication systems allow the user of a mobile terminal to conduct voice or video calls over a packet-based computer network, e.g. over an internetwork such as the Internet. Such communication systems include voice or video over internet protocol (VoIP) systems. These systems are beneficial to the user as they are often of significantly lower cost than conventional fixed-line or mobile networks, particularly for long-distance communication. Other types of communication media that can be implemented over a packet-based network include instant messaging (“IM”), SMS messaging, file transfer and/or voicemail.
When conducting communications such as VoIP calls over a first, packet-based network like the Internet, a mobile terminal typically connects to the Internet via a second, access network (which may also be packet-based in nature). If available, it is often possible to select between multiple different access networks. Typically a mobile terminal has two different types of connections available: wireless local area network (WLAN) and wireless wide area network (WWAN). Many WLANs typically use wi-fi, but other local, short-range wireless standards are also known in the art. The WWAN can be implemented by a number of different technologies such as GPRS, UMTS, HDPA, LTE, Wimax, etc. Usually, the type of WWAN available is decided by the operator, and as such the decision to make at the mobile terminal boils down to whether to use WLAN, WWAN, or both. On top of WLAN and WWAN, certain mobile terminals may have access to a satellite link as a third access technology, though this is usually a “last resort” if neither WLAN nor WWAN is accessible. In some systems it may also be possible to take into account a users' physical location in deciding whether to move to a network connection using a different wireless internet access technology.
To be able to choose which network to connect to, e.g. to select between WLAN or WWAN, or to select between two or more overlapping WLANs, the mobile terminal needs to know which networks are physically present and in operation. To do this the mobile terminal powers up its wireless interface or interfaces and listens for paging signals from potential networks. So if a mobile terminal comprises a short-range, local transceiver for communicating with a local area wireless network such as a wi-fi network, this is powered-up to listen for paging signals broadcast from the access points of any available WLANs; and if the mobile terminal comprises a longer-range cellular transceiver for communicating with a wide area wireless network such as a 3G or LTE network, this is powered-up to listen for paging signals from the base stations of the user's one or more WWAN providers. The relevant interface may then be powered down after a certain listening duration. This kind of process may be referred as a scan. Conventionally such scans are performed periodically, e.g. every few seconds or minutes, so that the mobile terminal always knows roughly what networks are available.